Well no xp, but you got the cavebear! That's pretty big early game. I think it's meant this way that you don't get any XP for taming monsters so it shouldn't show on the exit screen.

It seems to be tied to taming all oposing participants in a battle. While fighting multiple beasts and killing just one. All participants do get the XP and damage (including the newly tamed beasts, so if you have a big battle and want the XP kill something in the fight...)

Other effects are also erased including damage so no need to complain about dangerous either...

 
So agree with Kongdej that there is at least some kind of bug somewhere in that skill... (Here is guessing that its the erased results from a battle where all oposing forces are tamed...)